1. Field of the Invention:
This invention relates to improvement in the process of extraction of amino acids from aqueous solutions in which the amino acids are extracted with quaternary ammonium extrantant. In particular the invention relates to treatment to remove poisons which interfere with the overall extraction process and recovery of amino acid. Such poison removal treatment involves a pretreatment of the amino acid containing aqueous solution prior to extraction of the amino acid with the quaternary ammonium extractant and an acidic scrub treatment subsequent to the quaternary extraction to remove any remaining poisons. The pretreatment comprises an extraction of the aqueous solution with a tertiary amine to remove some of the impurities or poisons present along with the amino acids in the aqueous solution. The pretreatment extraction is carried out in a water immiscible organic solvent. This pretreatment removes the impurities leaving the amino acids in the aqueous solution for subsequent extraction with a water insoluble quaternary ammonium extractant. After extraction with the quaternary extractant, the organic phase is stripped of the amino acid and the stripped organic is subjected to an acidic scrub before being returned to the quaternary extractant stage.
2. Description of the Related Art
Extraction of amino acids using quaternary ammonium extractants can be seen from U.S. Pat. No. 4,661,606. As described therein amino acids are essential to animal and human nutrition and thus the production and purification of amino acids is an important procedure. Due to present industrial procedures it is necessary to remove amino acids from dilute fermentation broths and various aqueous mixtures. U.S. Pat. No. 4,661,606 describes a method by which the amino acids can be extracted from such dilute fermentation broths using water insoluble quaternary ammonium extractants dissolved in a water immiscible organic solvent. The amino acids are extracted from the aqueous phase into the organic phase, and due to the immiscibility of the two phases, these can be separated and the amino acids subsequently recovered from the organic phase (see FIG. 1). However, in the aqueous solutions containing the amino acids, there are other components present which interfere by complexing irreversibly with the extractant.
In co-pending U.S. application Ser. No. 864,064 filed May 16, 1986 a number of improvements in the process are described which involve various possible pretreatments of the fermentation broth before extraction with the quaternary ammonium extractant. Such pretreatments include ultrafiltration and/or an adsorption treatment. The ultrafiltration is useful in removing cellular materials present and other materials as described. The adsorption treatment utilizes materials such as clay or clay like materials, activated carbon and lime.
Another patent relating to purification of phenylalanine is U.S. Pat. No. 4,584,399. This patent discloses treatment of the phenylalanine containing aqueous solution, by ultrafiltration or centrifuging, to remove cellular material, contacting the filtered solution with an ion exchanger, such as a strongly acidic microporous resin, to absorb the phenylalanine, and eluting the absorbed phenylalanine.
While not related to recovery of amino acids South African Patent Application No. 84-6024 by Hoeschst Aktiengesellschaft relates to isolation of enzymatically produced carboxylic acids such as lactic acid and citric acid using an anion exchanger, i.e. polymer containing tertiary amino groups. The carboxylic acids are absorbed by the polymer containing the tertiary amino groups and then desorbed therefrom by treatment with a polar solvent from the group of aliphatic alcohols, ketones or carboxylic acid esters. Similarly U.S. patent 4,275,234 relates to a process for recovery of acids such as citric acid, lactic acid, oxalic and phosphoric acids from aqueous solutions by extraction with secondary or tertiary amines in a water immiscible organic solvent. The organic extract is then subjected to a stripping operation in which the acid is stripped from the organic into an aqueous stripping solution and the aqueous acid containing phase separated from the organic extractant phase.
Other patents and articles dealing with treatments of amino acids and materials or treatments related to this invention are:
______________________________________ U.S. Pat. Nos. ______________________________________ 3267029 3412018 3966594 4523999 4663048 3318867 4137405 4168268 3944606 4275234 4372923 3320024 4379126 4162230 3215622 ______________________________________